Gracilization of the Modern Human Skeleton

Bone is a remarkably dynamic tissue. Even after we reach adult
stature, our skeletons continue to change in response to metabolic
needs and mechanical stresses. Our author, a functional anatomist,
views human evolution through the lens of a growing body of
knowledge on how these needs and stresses shaped the structures of
bones in the fossil record. Ruff explains that even 5,000 years ago
(before much of the technology that insulates us from the physical
world), the bones of human beings were only half as strong as those
of human ancestors from several million years ago. Despite this
trend, our bones retain their ancient capacity to grow strong, such
that a long-time tennis player will have a playing-arm bone on
average 40 percent stronger than the bone in his non-playing arm.
This research sheds light on the causes and cures for osteoporosis,
and on the effects of weightlessness on astronauts.